Accumulation and Translocation of Heavy Metals in Hibiscus cannabinus Grown in Tannery Sludge Amended Soil

Digested sludge wasted by tanneries is rich in nutrients and trace elements however, the presence of toxic metals restricts their use in agriculture. The present study explores the possible application of tannery sludge amendment for the cultivation of an energy crop, Hibiscus cannabinus. The toxicity of various sludge amendments (25, 50, 75, and 100%, w/w) was examined during early seedling growth, followed by metal accumulation potential by performing pot experiments. Chemical characterization revealed the presence of Cr (709.6), Cu (366.43), Ni (74.6), Cd (132.71), Pb (454.8) μg.g-1 in tannery sludge beside N (2.1%), P 3.8 & K 316.96 (kg.hec-1.) respectively. Germination of H. cannabinus exposed to sludge extracts ranged between 80 to 95%; Relative seed germination, 81.33 to 84.43%. Relative root growth, 0.9 to 1.16 cm; and germination index, 95 to 110%. It was found that sludge extracts have not caused adverse effects on seed germination and early seedling growth. Heavy metal accumulation was observed as follows: Ni (3.37, 2.38, 1.46 & 0.90 mg.kg-1) > Pb (10.59, 10.15, 5.26, & 2.84 mg.kg-1) > Cu (2.34, 2.24, 0.97 & 0.24 mg.kg-1) > Cd (2.31, 1.19, 1.33 & 1.12 mg.kg-1) > Cr (1458, 1136.12, 601.73 & 211.6 mg.kg-1) in 100, 75, 50, & 25% sludge amended soil, respectively. The bio-concentration pattern of metals was found to be in the order of root > leaf > stem. The findings of the present study give direction for the eco-friendly and cost-effective management of tannery sludge. Further, H. cannabinus can be used for the restoration of metal-contaminated agricultural land, however, results need to be corroborated with field trials.